This invention relates to an ink jet recording apparatus comprising a recording head for jetting ink drops through nozzle orifices for recording and in particular to an ink jet recording apparatus intended for preventing a record image failure such as missing dots.
Some ink jet recording apparatuses such as ink jet printers, which will be hereinafter referred to as recording apparatuses, jet plural types of ink drops different in weight like micro dots, middle dots, and large dots through the same nozzle orifice to improve the image quality.
A recording head used with the recording apparatus comprises, for example, piezoelectric vibrator deformed by an applied waveform signal, pressure generating chambers expanded and contracted as the piezoelectric vibrator becomes deformed, and nozzle orifices communicating with the pressure generating chambers.
With such a recording apparatus, it is necessary to make a reasonable interval between waveforms. The time interval between the waveforms affects the image quality of a record image.
That is, if the time interval shifts from the optimum value, a record failure such as a heavy dot (a dot of a larger dot diameter than the original dot diameter) or a missing dot occurs.
To prevent the record failure, record patterns for causing the record failure to easily occur, for example, a one-line jetting pattern for jetting an ink drop of a large dot every eight nozzle orifices, a three-line jetting pattern for selecting three adjacent nozzle orifices every eight nozzle orifices and jetting an ink drop of a large dot through the selected nozzle orifices, and an alternate jetting pattern for jetting an ink drop of a large dot through the odd""th and even""th nozzle orifices alternately are actually recorded and evaluated with a recording head comprising 96 nozzle orifices per row, and the time interval between the micro dot and middle dot waveforms is determined based on the evaluation result.
However, although the time interval determined by evaluation with the record patterns is adopted, a record failure occurs in some cases.
For example, when the time interval between the micro dot and middle dot waveforms is determined based on the record patterns, if a pattern where the percentage of the nozzle orifices used for recording (recording density) is high, such as a one-line omission pattern, namely, a record pattern for setting a nozzle orifice for jetting no ink drop every eight nozzle orifices and jetting an ink drop of a large dot through the nozzle orifices except the setup nozzle orifice is recorded, the above-mentioned record failure occurs in some cases.
It is therefore an object of the invention to provide an ink jet recording apparatus for making it possible to lessen record failures if a record pattern having a high recording density such as a one-line omission pattern is recorded, thereby improving recording stability.
In order to achieve the above object, there is provided an ink jet recording apparatus comprising:
a drive signal generator for generating a drive signal including a first waveform component for jetting an ink drop to be a micro dot and a second waveform component for jetting an ink drop to be a middle dot;
a pressure generating chamber communicated with a nozzle orifice; and
a pressure generating element for varying the volume of the pressure generating chamber in accordance with the drive signal to jet an ink drop from the nozzle orifice.
An ink drop to be a large dot is jetted from the nozzle orifice when the first waveform component and the second waveform component are consecutively applied to the pressure generating element.
A time interval Txcexcm between an end point of the first waveform component and a start point of the second waveform component is set so as to substantially satisfy the following equation:       T    ⁢          xe2x80x83        ⁢    μ    ⁢          xe2x80x83        ⁢    m    =            n      2        ⁢    Tc  
here, Tc denotes a natural period of the pressure generating chamber, and n is an odd number of xe2x80x9c3xe2x80x9d or more.
Accordingly, propagation of vibration from the adjacent pressure generation chamber or the effect in the chamber caused by crosstalk of the piezoelectric element can be suppressed.
Thus, if a record pattern having a high recording density is recorded, recording failures can be lessened, thereby-improving the recording stability.
Preferably, n is set to 3.
Accordingly, the time interval Txcexcm becomes 1.5 times the characteristic vibration cycle of the pressure generating chamber Tc, so that the first waveform component and the second waveform component can be placed at a comparatively short time interval. Thus, to record a large dot, the remaining vibration after the first waveform component is applied can be used for jetting an ink drop of a middle dot, and the weight of the middle dot when a large dot is recorded can be made larger than the weight when the middle dot is recorded solely. Therefore, the ink drop weight range can be widened and recording can be executed in a wide dot diameter.
In order to attain the same effect, there is also provided an ink jet recording apparatus comprising:
a drive signal generator for generating a drive signal including a first waveform component for jetting an ink drop to be a micro dot and a second waveform component for jetting an ink drop to be a middle dot;
a pressure generating chamber communicated with a nozzle orifice; and
a pressure generating element for varying the volume of the pressure generating chamber in accordance with the drive signal to jet an ink drop from the nozzle orifice.
An ink drop to be a large dot is jetted from the nozzle orifice when the first waveform component and the second waveform component are consecutively applied to the pressure generating element.
When a frequency distribution of occurring a recording failure increases periodically as a function of a time interval Txcexcm between an end point of the first waveform component and a start point of the second waveform component, an actual Txcexcm is so as to avoid a value of which the frequency distribution increases.
In these apparatuses, the drive signal includes a third waveform component applied to the pressure generating element prior to the application of the first waveform component in order to finely vibrate a meniscus of the ink in the nozzle orifice.
Preferably, a time interval between an end point of the third waveform element and a start point of the first waveform element is set as a period in which the vibration caused by the third waveform element attenuates sufficiently.
Accordingly, jetting an ink drop by the first waveform component can be stabilized.
In these apparatuses, the pressure generating element is a piezoelectric vibrator formed into a combteeth shape in which electrodes and a piezoelectric body are laminated in a direction orthogonal to a deforming direction thereof.
Here, the time interval between the end point of the first waveform component and the start point of the second waveform component is not less than 3 Tc.
Accordingly, recording failures can be prevented more effectively.
In order to attain the same effect, there is also provided an ink jet recording apparatus comprising:
a drive signal generator for generating a drive signal including a first waveform component for jetting an ink drop to be a micro dot and a second waveform component for jetting an ink drop to be a middle dot;
a pressure generating chamber communicated with a nozzle orifice; and
a pressure generating element for varying the volume of the pressure generating chamber in accordance with the drive signal to jet an ink drop from the nozzle orifice,
wherein an ink drop to be a large dot is jetted from the nozzle orifice when the first waveform component and the second waveform component are consecutively applied to the pressure generating element, and
wherein a time interval between an end point of the first waveform component and a start point of the second waveform component is set so as to avoid ink ejection error.
Here, the time interval is represented as a function of a natural period of the pressure generating chamber.